Did you know when you make your royal icing that it is actually pretty transparent naturally? This can sometimes result in colors bleeding into each other when you ice cookies (i.e., red into white).
I add white food gel coloring into every single color I make. If I am making white royal icing, I add a good amount of white gel into it. If I am making any other color (besides black), I add white AND the other color. For example, if you were just to add red gel food coloring into your freshly made royal icing, sure it looks red but it's actually pretty transparent. White creates an opaque icing to get the most out of your final look! Don't let color bleeds get the best of you!
Where can you buy this? Americolor is my go-to color for cookie decorating, and is sold in many baking supply stores. Locally you can purchase it at Gygis and Bakers C & C. Americolor also sells directly from their website as well as on Amazon.